Thermionic valve



uvemtoz HORACE STJUHN 'DUNISTHURPE Feb. 2, 1932- H. ST. J. DE A. DONISTHORPE 'IIHERMIONIG VALVE Filed July 6, 1923 as n 1 0:

3 b omeglkkglffix Patented Feb. 2, 1932 UNITED STATES PATENT OFFICE HORACE ST. JOHN DE AULA DONISTHORPE, OF LONDON, ENGLAND, ASSIGNOR TO RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE THERMIONIC VALVE Application filed July 6, 1923, Serial No. 649,805, and in Great Britain July 14, 1922.

In the process of exhausting the bulb in the manufacture of a thermionic valve or the like, it is customary to heat the cathode in order that by the bombardment of the electrodes due to the emission of electrons from the cathode the gases occluded in the electrodes may be released so as to make the tube as hard as possible, and it frequently happens, especially in cases where the cathode is not completely surrounded by another electrode, that the glass of the bulb is damaged and pierced. This may be attributed to the bombardment of the glass by the ions produced by the collision of the electrons with the molecules of gas. The part of the bulb which is thus attacked and is liable to be pierced varies in different forms of valves and with the shape and disposition of the electrodes.

According to this invention, I apply a magnetic field to the tube during the process of exhaustion and bombardment in such a way as to prevent the concentration of the bombarding ions only to a very limited portion of the glass and to disperse them more or less over the surface of the glass so that undue heating and piercing of any particular portion of the glass is avoided. This I do by arranging a coil around or near the bulb and passing a current through the coil. The strength of the current and the arrangement of the coil will vary with different forms and types of tube and the particular arrangement of the coil and the strength of the current to be employed in any case may be judged by the blue glow due to the ions.

By Way of example, the invention is illustrated by the accompanying drawings in which Fig. 1 illustrates the manner in which the ions are concentrated around the neck of the bulb in one type of thermionic valve.

Fig. 2 shows the manner in which the path of the ions is changed by the application of a coil surrounding the bulb.

Fig. 3 shows a further modification in which an electromagnet is arranged at one side of the bulb.

Fig. 4 shows a further modification in which the field is created by means of a coil surrounding the pump connection of the valve.

Fig. 5 shows a suitable form of circuit connections.

In a valve of the type shown in Figure 1 the general direction of the ionic stream as evidenced by the blue glow is shown by the dotted lines. It will be seen that the stream of ions is concentrated on to and around the neck of the bulb and in consequence of this concentration the glass of the neck is apt to be pierced.

F igure 2 shows a coil A arranged around the bulb so as to produce a magnetic field, the lines of magnetic force being represented by the dotted lines. The ions follow the lines of magnetic force and in consequence are distributed over the surface of the glass instead of being concentrated on any particular region and therefore the danger of damage to the glass is very considerably reduced.

Figure 8 shows an electro-magnet A arranged at one side of the bulb. Here again the dotted lines represent the lines of magnetic force and it will be noticed that as in the arrangement of Figure 2 the ions which follow these lines are distributed and there is no concentration of the ions on any particular part of the glass.

The strength of the magnetic force required with any particular type of valve can readily be found by trial and in order that this force may easily be varied it is convenient to connect a variable resistance in series with the coil.

Figure 5 is a diagram of the connections when a coil such as that shown in Figure 2 is employed. The coil A is connected through a variable resistance R to a battery 13. P is the anode or plate of the valve connected through a high tension battery H to the filament F which is heated by a battery D. G is the grid and C is the connection to the pump.

In some cases I may arrange a coil A around the connection C as shown in Figure a so that the lines of force are as indicated by the dotted lines, and the time required to exhaust the valve may be reduced.

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Having described my invention what I claim is: I

1. The method of removing occluded gases from a metallic mass in an envelope which consists in bombarding the mass by an electron stream and directing the resulting stream of ions magnetically away from the mass.

2. The method of removing occluded gases from an electrode in an envelope which consists in bombarding the electrode by an electron stream and dispersing the resulting stream of ions by a magnetic field to prevent concentration thereof on particular portions of the enveloping surface.

3. The method of removing occluded gases from an electrode in an envelope which consists in bombardingithe electrode'by an electronstream during the evacuation of the envelope and dispersing the resulting stream ofions magnetically to prevent injury to the envelope.

4:- The process of evacuating a bulb which comprises subjecting the metal parts inside the bulb to an electronic bombardment and magnetically directing theresulting stream of ions from the outside of said bulb.

5. The process of exhausting a tube which includes the step of bombarding portions of the tube by an electron stream, and thereafter dispersing the energy stream which has resulted from the bombardment, said dispersing process including the step of producing a magnetic field in proximity to the tube.

HORACE ST. JOHN de AULA DONISTHORPE. 

